The Ice Trolls (and their Veteran versions as well) appear to be bugged - when you hit them with a stun (such as from Steal Time), there seems to be a significant chance (my testing shows about one in four) that they will remain stationary and not attacking even after the duration of the stun wears off - even if attacked.
"Not all those who wander are lost." J.R.R. Tolkien
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